EHV circuit breaker utilizing gallium cathode ignitrons for synchronous closing

ABSTRACT

A gallium cathode high voltage ignitron for synchronous closing of EHV circuit breakers, is provided, to control switching surge overvoltages. Due to the fast triggering time of the gallium cathode ignitron the circuit can be closed synchronously without pre-insertion resistance to obtain a switching surge level of 1.5 per unit or less.

United States Patent Yoon et al. 1 June 24, 1975 1541 EHV CIRCUlTBREAKER UTILIZING 3.299.377 1/1967 (211C114 ct =11 200/148 1 GALLIUMCATHODE IGNITRONS FOR 2 OX SYNCHRONOUS CLOSING 3,646,295 2/1972 Circle317/11 A [75] Inventors: Kue H. Yoon; Robert E. Friedrich;

Andreas M. Sletten, all of Pittsburgh. Primary Examiner-Robert S. Macon[73] Assignee: Westinghouse Electric Corporation, Almmey Agent MassungPittsburgh, Pa.

[22] Filed: May 4, 1973 1211 Appl. No.: 357,437 [57] ABSTRACT 1521 us.c1..... 200/144 AP; 200/144 B; 200/148 1; A gallium cathode high voltagsignilron for 51991119 317/1 1 A nous closing of EHV circuit breakers, isprovided, to 1511 1111.131. 1. HOlh 33/16 control Switching Surgeovervolwges- Due to the f 158] Field of Search 200/144 AP, 144 B, 143 1;triggering time f e g i m h de igni ron. th cir- 317 1 1 A, 1 1 B 1 1 Q1 1 1 1 1 E cuit can be closed synchronously without pre-insertionresistance to obtain a switching surge level of 1.5 per [56] ReferencesCited Unit less- UNlTED STATES PATENTS 2,665,396 1/1954 Weinfurt 317/1 1A 10 Claims, 5 Drawing Figures 10 i 26 I 12 1 fi l EHV CIRCUIT BREAKERUTILIZING GALLIUM CATIIODE IGNITRONS FOR SYNCHRONOUS CLOSING BACKGROUNDOF THE INVENTION This invention relates generally to circuit breakersand more particularly to high voltage circuit breakers having a meansfor closing the circuit breaker synchro nously at the instant thevoltage across the contacts is substantially zero or a minimum.

In determining the insulation requirements for transmission equipment,consideration must be given to the voltage levels to which variousinsulation systems will be subjected. Normal operating voltages,switching surges and lightning surges must all be considered. Asreported in I.E.E.E. transactions on Power Apparatus and Systems, VolumePAS-88, No. 7, July, 1969 in an article entitled Multi-Step ResistorControl of Switching Surges" by R. G. Colclaser, Jr., charles L. Wagnerand Edward P. Donohue on pages 1022 to 1023: Prior to the advent of 500KV systems, lightning was the criterion governing the number ofinsulators required for transmission lines. During the engineeringstudies for the Virginia Electric and Power Co. 500 KV System it wasfound that switching surges were a determining factor; for example,switching surges produced by conventional breakers dictated that 35insulators were needed, whereas from a lightning standpoint only 24insulators were required. At this point the concept of single steppre-insertion resistor switching to reduce the maximum switching surgefrom 3.0 per unit to approximately 2.0 per unit was instituted. Withthis switching surge reduction, lightning again becomes the determingfactor for line insulation. All domestic 500 KV breakers are nowsupplied with the single step resistor feature. Recent studies on UHVsystems show that to keep the line insulation down to the lightninglevel at system voltages above 500 KV, further reduction in switchingsurge magnitudes may be indicated. At 765 KV, for example, maximumswitching surge levels of 1.7 pu may be required, at 1,100 KV, levels of1.5 pu or lower may be needed."

When an open transmission line is energized by closing power circuitbreakers depending on the initial voltage across the breaker contacts,the switching surge voltage can be quite high. As stated above, this isespecially true for the extra high voltage class (EHV) breakers and theultra-high voltage class (UHV) breakers. Switching surge voltagesdeveloped can easily flash over insulators or destroy the lineinsulation system. To construct an insulating system to withstand thesurge voltages the cost may become prohibitive or may even be impossibleto attain physically in the case of 765 or 1,100 KV class, unless somemeans are provided to control the switching surge voltage level.

The most direct method to control the switching surge level is byclosing the circuit breaker synchronously at the instant when thevoltage across the contacts is substantially zero or a minimum. Thesynchronous closing can be achieved with or without preinsertion ofresistance. However, the closing of an EHV or UHV power circuit breakerinvolves the motion of heavy masses and ultra-high speed contactmovement. In practice, synchronous closing of the main power contacts isnot possible. A study was carried out to examine the switching surgevoltage levels taking the random variation of breaker closing intoconsideration. It

was determined that to obtain a switching surge level of 1.5 per unit orless 98 percent of the time, with a maximum level of 1.65 per unit, thestandard deviation for the closing without resistance must be limited toabout 13 (0.602 milliseconds). It was also determined in order to obtaina switching surge level of 1.5 per unit or less percent of the time,with a maximum level of 1.65 per unit utilizing pre-insertion of a 450ohm resistance, the standard deviation should be limited to ap'proximately 30 (1.39 milliseconds).

At present, closing a 550 KV breaker requires approximately 6% cycles(108 milliseconds) and the above closing requirements are quitedifficult to meet. Although manufactures are trying to meet theserequirements by improved closing mechanisms and also by using optimumresistance values it is desirable to have an alternate means ofsynchronously closing power circuit breakers. This is especially truewhen the trapped charge voltage on the line fluctuates due tooscillations with the compensating inductors, necessitating a rapidsynchronization.

Presently 550 KV SF, gas filled circuit breakers, with two pre-insertionresistors, are designed to limit surges during closing to 1.5 per unitfor 98 percent of the operations with an absolute limit of 1.65 perunit. It is therefore desirable to have a circuit breaker, with meansfor synchronously closing the electric circuit at a minimum voltage orsubstantially zero, which limits the surge voltage below the 1.5 perunit level most of the time, with an absolute limit of 1.65 per unit.

SUMMARY OF THE INVENTION In accordance with the invention, an EHV or UHVcircuit breaker is provided including a high voltage gallium acathodeignitron for synchronous closing of the circuit breaker, to limit theswitching surge voltage, without insertion of resistance before closingthe main circuit breaker contacts. The gallium cathode ignitron isconnected in parallel with the contacts of the high voltage circuitbreaker. The gallium cathode ignitron is triggered and closes thecircuit breaker circuit at a voltage minimum or zero just precedingclosing of the main breaker contacts. Thus, when the main contactsclose, the circuit has already been closed synchronously and noswitching surges are produced.

The cathode of the ignitron can be pure gallium, gallium mixed with someother material to lower the freezing point, or gallium absorbed in asieve of some refractory material. The gallium cathode ignitron can bemade to conduct high currents and to withstand extremely high voltages.Gallium has a high boiling point, a low melting point and low vaporpressure; thus, the liquid gallium can be used as a cathode and cathodeerosion problems can be eliminated. The gallium cathode ignitron alsohas a very rapid ignition time. The initiation of full currentconduction can be made in terms of a few microseconds.

As the voltage levels of transmission systems increase, the switchingsurge control problem is becoming more acute from the standpoint ofeconomics and physical capability of the insulation systems. Theapplication of the gallium cathode high voltage ingitron to thesynchronous closing of high voltage circuit breakers can solve manyproblems by controlling the switching surge overvoltages.

The gallium cathode ignitron described in the present application canhave a gallium pool cathode, a triggering electrode, a molybdenum anode,all disposed in an evacuated housing having a high vacuum below 2 X ITorr. Although the invention is described using ignitrons with liquidgallium cathodes, it should be understood that for circuit breakerclosing application it is possible to use solid cathodes in theignitrons since the number of operations by the ignitrons will be smalland thus erosion of the cathode limited. There are also other liquidcathodes, alloys of gallium, which have certain advantages. Anexperimental model has been built showing withstand boltage betweenanode and cathode of greater than [20,000 volts. Practical devices witha withstand voltage greater than 300,000 volts can be built. It has beenshown experimentally that triggering can be attained consistently withintwo microseconds, with an anode voltage as low as 25 volts and atriggering voltage of l0,000 volts. In an expermental gallium cathodeignitron currents of 1,000 amps can be conducted for 25 millisecondsrepeatedly with no visible damage to the tube, and currents of at least20,000 amps can be conducted for periods of several microseconds withoutdamage. The voltage drop across the gallium ignitron during conductionof currents is about volts. After initial pulse triggering, the anodecurrent continues to flow after the triggering signal is removed, untilthe next voltage zero or until the anode current is removed. The galliumpool in the gallium cathode ignitron need not be in the liquid state inorder for the device to operate successfully. For repeated operationswith high current, however, it is desirable that the cathode beliquified occasionally to reform a smooth cathode surface and to returncondensed cathode material from walls and anode to the cathode region.

The gallium cathode ignitron can be applied to synchronous closing ofhigh voltage circuit breakers with or without the pre-insertionresistance. However, because of the fast triggering time of the galliumignitron, the l,5/l.65 per unit switching surge ratio conditions can besatisfied even without the pre-insertion resistance. Thus, using thegallium cathode ignitron, the necessity for the pre-insertion ofresistance before main circuit breaker contact closing can beeliminated.

In one embodiment of the invention, two gallium cathode ignitrons areput inside the high voltage breaker housing. Each ignitron has its owntriggering circuit so that the synchronous closing can be achieved ateither polarity of the terminal voltage, but the ignitron under oppositepolarity would definitely not fire. A sensing and control circuit candetermine the polarity as well as the voltage zero to select the righttriggering circuit. One of the ignitrons is fired at the voltage zeropreceding the closing of the main contact, by not more than A cycle. Forinstance, the closing of the main contact can be aimed at the middle ofa half-cycle of the terminal voltage wave. The main contacts can beaimed to close at between 6 and 6% cycles. Thus a fairly large deviationfor the main contact closing of the power circuit breaker can betolerated.

An alternate operation using both ignitrons would be to continuallytrigger both ignitrons from any voltage zero prior to main contactclosing. If two ignitrons are used and triggered so as to giveconduction in both directions from the time of a given voltage zeroacross the mechanical contacts, then the mechanical contacts can beclosed randomly without any need for mechanical synchronization. Such amode of operation could result in a cheaper mechanical drive system forthe breaker.

As stated hereinbefore, the gallium cathode can be activatedconsistently within 2 microseconds after triggering. The triggeringcircuit can be resistancecapacitor (R-C) or inductive coupling circuitscombined with trigatrons, thyratrons, or ignitrons, which arecommercially available, and can be made to trigger within a fraction ofa microsecond.

A single gallium ignitron can be used for synchronously closing thecircuit breaker provided the main contact is aimed to close during thathalf of the voltage wave for which the ignitron can conduct. If only oneignitron is used, the sensing and control circuit can be designed tooperate at only one polarity and V2 of the triggering circuit can beeliminated. For multi-break circuit breakers, the configurationdescribed above can be multiplied accordingly.

In another variation, rather than place the gallium cathode ignitronsinside of the circuit breaker they can be disposed external thereto. Thegallium ignitrons should normally be mounted inside of the high voltagegas SF, circuit breaker, to take advantage of the high dielectricstrength of the SF environment. However, with improved construction ofignitrons, they can be located external to the circuit breaker if it ismore convenient.

In the case of a fluctuating trapped charge voltage on the line due tocompensating inductance, sensing of the line and bus voltages arenecessary, to send a triggering pulse near a zero terminal voltage. Thatis, the gallium cathode ignitron is fired at the instant in time whenthe bus voltage equals the voltage existing on the open line, so thatthe voltage across the high voltage circuit breaker is approximatelyzero.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention reference may be had to the preferred embodiments, exemplaryof the invention shown in the accompanying drawings in which:

FIG. 1 is a schematic diagram of an electrical system using a circuitbreaker having a gallium cathode ignitron for synchronous closing;

FIG. 2 is a graphic representation of a closing sequence for a highvoltage circuit breaker utilizing the teachings of the presentinvention;

FIG. 3 is a side sectional view of a gallium cathode ignitron;

FIG. 4 is a side view, partially in section, of a high voltage circuitbreaker having internally mounted gallium cathode ignitrons; and

FIG. 5 is a side view of a portion of a high voltage circuit breakerhaving externally mounted gallium cathode ignitrons.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsand FIG. 1 in particular, there is shown a schematic diagram of anelectrical system having a high voltage circuit breaker 10 utilizing theteachings of the present invention. As shown in FIG. 1, an alternatingcurrent generator 12 supplies a bank of step-up transformers 14, theoutput of which is connected to a high voltage circuit breaker 10. Theoutput of the high voltage circuit breaker l0 feeds a transmission lineand load whose electric parameters are represented schematically bycapacitance 15, in-

. t; is 6 duct-ance l6 and resistance [7. A gallium ignitron 20 isdisposed within the housing of the high voltage circuit breaker 10. Abus boltage V is present on the bus side, the terminal being fed by, thevoltagesource 12,. of the high voltage breaker 10. A line voltage V 'ismeasured on the line side, the terminal feeding the transmission line,of the high voltage breaker 10. A potential sensing device 19 and acontrol device 18 are connected to monitor the bus voltage VPotentialsensing device 19 feeds a voltage proportional to the busvoltage to control device l8. Control device 18 which can be similar tothe timed closing device described in IEEE Paper 71 TP 571 -PWR,entitled EHV Breaker Rated for Control of Closing Voltage SwitchingSurges to 1.5 Per Unit." has a low burden. If available existingpotential devices, such as potential transformers or capacitive bushingtaps. can supply the reference voltage to control device 18.

When pushbutton 22 is depressed, indicating that the high voltagebreaker is to be closed, control device 18 energizes the circuit breakerclosing coil 24 at the proper time for the main contacts to close aftera predetermined number of cycles. Thus the main contacts 26 of circuitbreaker. 10 will close within a given cycle period, several cycles afterthe closing coil is energized. If the main contacts 26 are aimed toclose at the peak of a given /5 cycle there can be a plus or minusonequarter cycle l .4 millisecond) deviation and the main breakercontacts 26 will still close in the desired A cycle. The requirement ofclosing of the main contacts within 4 milliseconds of a voltage zero caneasilybeaccomplishecd by controlling the time with respect to voltagezero at which theclosing coil 24 is energized.

tron 20, initiating conduction of the gallium cathode A delay mustnormally be added to the breaker closing time so that the delayedclosing time will result in the main contacts closing duringthe desired,2 cycle. The initiating and delaying function is performed by controldevice 18. At the beginning of the i cycle during which the maincontacts 26 will close, the control .de-

cathode ignitron 20 is connected in parallel withthe main contacts 26 sothat the circuit completed by high voltage breaker 10 can be closed verynear a voltage zero, by proper triggering of the gallium cathodeignitron 20.

Referring now to FIG. 2, there is shown a graphic representation of aclosing sequence. At some point in time as indicated at 29 pushbutton 22is actuated indieating to control device 18 that it is desired to closethe circuit breaker 10. Device 18 senses the first voltage zero 30 afterpushbutton 22 is actuated at time 28. A predetermined time A I later,control device l8'energizes the closing coil 24. The time delay A rbeforeenergizing the closing coil is determined so that the main breakercontacts 26 will close in the desired cycle following a predeterminedtime, indicated by arrow 32, after the first voltage zero 30. The maincontacts 26 are aimed to close at the peak 34 of half-cycle 3,3. Closingof the main contacts 26 at any point within the halfcycle 33 issatisfactory, thus by aiming. the, main contacts 26 to close at the peakpoint 34, the contact closing can deviate onefourth cycle around 34 andstill be satisfactory. At the beginning of half-cycle 33, a triggeringpulse 36 is supplied to the gallium cathode igniignitron 20. Thus, themain contacts 26 close during the half cycles 33 when the galliumcathode ignitron 20 is conducting. The only voltage across contacts 26during final closing is the small voltage drop across the conductinggallium ignitron 20. The voltage drop across the gallium cathodeignitron 20 during conduction will be in the order of 20 volts. Thegallium ignitr on 20 starts conducting rapidly so that the circuitthrough the high voltage circuit breaker 10 is closed at essentially avoltage zero.

Referring now to FIG. 3, there is shown a side view partially in sectionof a gallium cathode ignitron 20. Conventional ignitrons uses a mercurypool as cathode and since mercury has a high vapor pressure, thewithstand voltages are limited to about 20 KV for repetitive operation.Higher operating voltages are achieved in mercury arc tubes where gridsare introduced to maintain a more even field distribution but their sizeand cost increase rapidly with increasing voltage. The currentcapability of mercury tubes which is severly limited by the vaporpressure requires forced cooling for higher power limits. Gallium has avery low vapor pressure at room temperature with a vaporpressuretemperature profile almost identical to that of silver. Thus, incontrast to mercury, the break-down characteristics of a galliumignitron 30 or rectifier are in the ultra-high vacuum breakdown regionsand a small gap should be sufficient to withstand high voltages. inaddition gallium is a liquid at room temperature (melting point 298C)but supercools for a very long period of time under vacuum. Thus, likemercury, cathode erosion under continual arcing is eliminated. A galliumcathode ignitron 20 can handle currents of several thousand amps with noapparent difficulty. Pressure within the gallium ignitron 20 can belowered to and remains below 2 X l0" Torr, and shows no tendency .toincrease even after heavy current pulses. The gal- ;must be exercised inthe construction of an ignitron containing liquid gallium. [n thegallium ignitron 20, a .quartz beaker 40 is used to contain the galliumcathode pool 42. A tungsten rod 44 dipping into the gallium pool 42,serves as an electrical cathode connection. Quartz and tungsten are twoof the materials showing most resistance to attack by liquid gallium.The anode I 46 ,is formed from molybdenum and is connected to areentrant type glass bushing 48. The glass bushing 48 is supported froma stainless steel flange 50 which is connected to a stainless steel topcap 52. The quartz beaker 40 is suspended from the top cap 52 and con-.tains approximately 300 grams of gallium, which forms a cathode pool42. A glass envelope S4 is joined to stainless steel flange 56 in avacuum tight relationship. Stainless stell flange 56 is attached to topcap 52 using a gold gasket for a vacuum tight seal. When top cap 52 isjoined to flange 56 glass envelope 54 surrounds the quartz beaker 40.The trigger electrode 58 passes through an opening 60 in top cap 52.Trigger electrode 58 is constructed from molybdenum. Trigger electrode58 is supported by ceramic bushing 62 which is joined to the top cap 52in a vacuum type relationship. The bottom portion 64 of the triggerelectrode 58 is a tungsten rod ground to a fine point 66, at one end,and maintained at a height which is approximately I millimeter above thegallium pool 42.

Referring now to FIG. 4, there is shown a high volt age circuit breaker10 having two gallium ignitrons disposed therein. A potential device 19feeds a voltage proportional to the bus voltage to the control device18. Device 18 has a low burden; thus the potential device 19 can becapacitive or inductive low power potential source to supply thereference voltage. The signal required by device 18 could also beobtained from an existing potential device which the user may alreadyhave in service. The circuit breaker 10 shown in FIG. 4 represents onepole of a three-phase alternating current circuit breaker. The circuitis made through con ducting studs 72 which pass through the bushings 74and terminate on stationary contacts 76. A rotating bridging contact 78makes contact with stationary contacts 76 and completes an electricalcircuit between contacts 76. Operating rod 80 is mechanically linked torotatable contact 78 and is used to rotate contact 78 between a firstposition in engagement with contacts 76 and a second positionn separatedfrom contacts 76 to thereby interrupt the circuit through circuitbreaker 10. Contact 78 is moved to the closed position by energizingclosing coil 24 which moves operating rod 80 so as to close the circuitbreaker 10. When it is desired to close the circuit breaker [0, thepotential sensing device 19 and control device 18 senses the firstvoltage zero after circuit closing is indicated and at the proper timeenergizes closing coil 24 so that the main contacts 76 and 78 closes ina known half-cycle at a predeter mined future time. At the beginning ofthe half cycle during which the movable contacts 78 will close, atriggering signal 36 is sent to the proper gallium ignitron 20 andcompletes the circuit through breaker 10. Thus the circuit is madethrough circuit breaker 10 at or very near a voltage zero. The galliumignitron 20 conducts during the half cycle in which the main movingcontact 78 engages stationary contacts 76 to mechanically complete thecircuit. After the end of the half cycle during which the movablecontact 78 closes, the gallium ignitron 20 ceases conduction.

In the embodiment of the invention shown in FIG. 4, the galliumignitrons are disposed within the housing 82 of the high voltage circuitbreaker 10. If the breaker 10 is of the SF variety, the galliumignitrons 20 being disposed within the housing 82 can take advantage ofthe SF, environment and its high dielectric strength. Triggeringelectrode lead 84 passes through a bushing 86 in housing 82 and connectsto the trigger electrode 58.

Potential device 19 is connected to the source or bus side of the highvoltage circuit breaker 10. When there is a trapped charge voltage onthe line which fluctuates because of the oscillation with thecompensating inductors, a fast synchronization is mandatory. In the caseof a fluctuating trapped charge voltage on the line, an additionalpotential sensing device 88 is required. The signals from line potentialdevice 88 and from bus potential device 19 are transmitted to controldevice 18 so that the triggering pulse 36 to the appropriate galliumcathode ignitron 20 can be transmitted near a zero terminal voltage,across circuit breaker contacts 76 and 78. When a fluctuating trappedcharge voltage is present on the line, because of the compensatinginductance, an additional sensing of the line voltage is necessary priorto the mechanical contact closing to send the triggering pulse 36 whenthe voltage across contacts 76 and 78 is zero or at a minimum. Controldevice 18 compares the signals from potential device I9 and potentialdevice 88 and sends a signal to the proper gallium ignitron 20 so thatit begins to conduct at or near the point where the instantaneous busvoltage equals the voltage on the line, at this point the voltage acrossthe open breaker contacts is essentially zero. Thus, the circuit iscompleted at a voltage zero in the one-half cycle before the closing ofthe main contacts 76 and 78. That is, the circuit is completed when thebus voltage V equals and is in phase with the voltage existing on theopen line V and the voltage across circuit breaker I0 is approximatelyzero. Control device 18 through potential sensing device monitors theline voltage V, under all conditions of do. trapped charge and a.c.oscillations, for shunt reactor compensated lines, and fires the galliumignitron 20, which rapidly conducts within two microseconds of receiptof the signal, in the one-half cycle preceding contact 76 and 78closing.

FIG. 5 shows a portion of a circuit breaker 10, as shown in FIG. 4, butwith gallium ignitrons mounted external to the circuit breaker 10.Operation of the gallium ignitron 20 and the related components is asdescribed above. The gallium ignitrons 20 as described above were putinside the circuit breaker I0 to utilize the high dielectric strength ofthe SP However, with improved construction of gallium ignitrons 20 theycan be used external to the breaker, if this is more convenient. Byusing the gallium ignitrons external to the breakers, it is notnecessary to bring in the triggering leads 84 through the interrupterhousing 82 and the gallium ignitrons can be applied to existing highvoltage breaker designs without any modification of the circuit breaker10.

From the description given above it can be seen that the gallium cathodeignitron 20 can be applied to the synchronous closing of EHV or UHVbreakers to control the switching surge voltage. The switching surgevoltage can be controlled without pre-insertion of closing resistors. Bycompleting the circuit at or very near a voltage zero, which is possibledue to the fast triggering time of the gallium ignitron 20, a 1.5 normal1.65 maximum switching surge ratio condition can be acheived withoutpre-insertion resistance.

We claim:

1. A high voltage synchronous closing circuit breaker for use on analternating current circuit above I00 KV, comprising:

a housing,

main contact means disposed in said housing and being movable between anopen and a closed position;

synchronous closing means connected in parallel with said main contactmeans for synchronously closing at substantially the voltage zero justprior to main contact closing and thereby completing an electricalcircuit around said main contacts;

said synchronous closing means comprising a gallium cathode ignitronmeans having an anode, a cathode and a trigger disposed within a sealedhousing; said anode directly connected to one side of said main contactmeans and said cathode directly connected to the other side of said maincontact means;

said gallium cathode ignitron means constructed to have greater than amo KV withstand level thereacross;

trigger actuating means connected to said trigger to trigger saidgallium cathode ignitron within 100 microseconds of a voltage zero.

2. A high voltage synchronous circuit closing circuit breaker as claimedin claim 1, including: multiple gallium cathode ignitrons connected inparallel with said main contact means, at least one of said multiplegallium cathodes being connected in a positive polarity connection andat least one of said multiple gallium cathode ignitrons connected in anegative polarity connection, so as to be capable of completing acircuit of either polarity across said main contact means.

3. A high voltage synchronous closing circuit breaker as claimed inclaim 2 wherein said gallium cathode ignitrons are disposed internallyof said circuit breaker housing.

4. A high voltage synchronous closing circuit breaker as claimed inclaim 2 wherein said gallium cathode ignitrons are disposed external tosaid circuit breaker housing.

5. A high voltage synchronous closing circuit breaker as claimed inclaim 2, wherein said synchronous closing means comprises: means forsensing the voltage across said main contact means; and means fortriggering said gallium cathode ignitron into conduction at a voltagezero across said main contact means at the beginning of the one-halfcycle during which said main contact means close to limit closing surgevoltage.

6. A high voltage synchronous closing circuit breaker as claimed inclaim 1, wherein said gallium cathode ignitron comprises: a cathodeformed from gallium; an anode displaced from said cathode to form a gaptherebetween', a trigger electrode cooperatively associated with saidanode and said cathode to initiate an electrical conducting path betweensaid anode and said cathode when energized, and a highly evacuatedhousing surrounding said anode, said cathode and said trigger electrode.

7. A high voltage synchronous closing circuit breaker as claimed inclaim 6, wherein: said gallium cathode is supported in an insulatingcup-shaped member; and said evacuated housing comprises, a glasscup-shaped portion, a metal top cap joined to said glass cup-shapedportion in a vacuum-tight relationship, said metal top cap having a holetherethrough for passage of said anode, said anode being electricallyinsulated from said top cap, and a tungsten rod having one end attachedto said top cap and having the other end immersed in said galliumcathode so as to electrically connect top cap to said gallium cathode.

8. A high voltage alternating current synchronous closing circuitinterrupter for use on EHV circuits above 69 KV, comprising:

a housing which is sealed;

an insulating gas disposed within said sealed housing;

main contact means disposed in said housing, movable between an open anda closed position;

a plurality of synchronous closing means for synchronously closing at avoltage zero prior to main contact closing and thereby completing anelectrical circuit around said main contacts disposed within saidhousing and being surrounded by said insulation gas;

each of said plurality of synchronous closing means comprises a galliumcathode ignitron having an anode, a cathode, and a trigger disposedwithin an evacuated housing; and,

each of said gallium cathode ignitrons constructed to have a withstandvoltage level above 69 KV and a trigger time of less than 20microseconds.

9. A high voltage alternating current synchronous closing circuitinterrupter, as claimed in claim 8, wherein:

each of said plurality of synchronous closing means comprises anignitron having a cathode; and

said cathode comprises gallium.

10. A high voltage alternating current synchronous closing circuitinterrupter, as claimed in claim 8, wherein:

said insulating gas comprises sulfur hexafluoride.

1. A HIGH VOLTAGE SYNCHRONOUS CLOSING CIRCUIT BREAKER FOR USE ON ANALTERNATING CURRENT CIRCUIT ABOVE 100 KV, COMPRISING: A HOUSING, MAINCONTACT MEANS DISPOSED IN SAID HOUSING AND BEING MOVABLE BETWEEN AN OPENAND A CLOSED POSITION, SYNCHRONOUS CLOSING MEANS CONNECTED IN PARALLELWITH SAID MAIN CONTACT MEANS FOR SYNCHRONOUSLY CLOSING AT SUBSTANUALLYTHE VOLTAGE ZERO JUST PRIOR TO MAIN CONTACT CLOSING AND THEREBYCOMPLETING AN ELECTRICAL CIRCUIT AROUND SAID MAIN CONTACTS;
 2. A highvoltage synchronous circuit closing circuit breaker as claimed in claim1, including: multiple gallium cathode ignitrons connected in parallelwith said main contact means, at least one of said multiple galliumcathodes being connected in a positive polarity connection and at leastone of said multiple gallium cathode ignitrons connected in a negativepolarity connection, so as to be capable of completing a circuit ofeither polarity across said main contact means.
 3. A high voltagesynchronous closing circuit breaker as claimed in claim 2 wherein saidgallium cathode ignitrons are disposed internally of said circuitbreaker housing.
 4. A high voltage synchronous closing circuit breakeras claimed in claim 2 wherein said gallium cathode ignitrons aredisposed external to said circuit breaker housing.
 5. A high voltagesynchronous closing circuit breaker as claimed in claim 2, wherein saidsynchronous closing means comprises: means for sensing the voltageacross said main contact means; and means for triggering said galliumcathode ignitron into conduction at a voltage zero across said maincontact means at the beginning of the one-half cycle during which saidmain contact means close to limit closing surge voltage.
 6. A highvoltage synchronous closing circuit breaker as claimed in claim 1,wherein said gallium cathode ignitron comprises: a cathode formed fromgallium; an anode displaced from said cathode to form a gaptherebetween; a trigger electrode cooperatively associated with saidanode and said cathode to initiate an electrical conducting path betweensaid anode and said cathode when energized, and a highly evacuatedhousing surrounding said anode, said cathode and said trigger electrode.7. A high voltage synchronous closing circuit breaker as claimed inclaim 6, wherein: said gallium cathode is supported in an insulatingcup-shaped member; and said evacuated housing comprises, a glasscup-shaped portion, a metal top cap joined to said glass cup-shapedportion in a vacuum-tight relationship, said metal top cap having a holetherethrough for passage of said anode, said anode being electricallyinsulated from said top cap, and a tungsten rod having one end attachedto said top cap aNd having the other end immersed in said galliumcathode so as to electrically connect top cap to said gallium cathode.8. A high voltage alternating current synchronous closing circuitinterrupter for use on EHV circuits above 69 KV, comprising: a housingwhich is sealed; an insulating gas disposed within said sealed housing;main contact means disposed in said housing, movable between an open anda closed position; a plurality of synchronous closing means forsynchronously closing at a voltage zero prior to main contact closingand thereby completing an electrical circuit around said main contactsdisposed within said housing and being surrounded by said insulationgas; each of said plurality of synchronous closing means comprises agallium cathode ignitron having an anode, a cathode, and a triggerdisposed within an evacuated housing; and, each of said gallium cathodeignitrons constructed to have a withstand voltage level above 69 KV anda trigger time of less than 20 microseconds.
 9. A high voltagealternating current synchronous closing circuit interrupter, as claimedin claim 8, wherein: each of said plurality of synchronous closing meanscomprises an ignitron having a cathode; and said cathode comprisesgallium.
 10. A high voltage alternating current synchronous closingcircuit interrupter, as claimed in claim 8, wherein: said insulating gascomprises sulfur hexafluoride.